computer integrated machine design
TRANSCRIPT
COMPUTER INTEGRATED MACHINE DESIGN
Charles E. Wilson New Jersey Institute of Technology
Prentice Hall Upper Saddle River, New Jersey Columbus, Ohio
Contents
Preface xxv
Chapter 1 Creative Design 1
Computer-Aided Engineering (CAE) 2 Concurrent Engineering (CE) 2
Computer-Aided Drafting (CAD) 3
Wire-Frame Models 4
Creation of a Solid Model 4 Extrusion 6
Revolving a Profile 6 Skinning 6 Construction Operations (Boolcan Operations) 6
Design Implications 6 Properties 11
Center-of-Gravity 11 Mass-Moment-of-Inertia 12
Selectmg Software: Choosing Among Programming Language, Spreadsheets and Equalion Solvers (Mathematic Software) 15
Newton's Laws and Related Principles 16 D'Alembert's Principle 17 Moment and Torque Equilibrium 17 Free-Body Diagrams 17 Stress and Strain 18 Determination of Material Properties 18 Analytical Methods for Finding Stresses and Deflections 20 Finite Element Analysis (FEA) 20 Factor of Safety 22
viii * Contents
Optimum Design 23 Problems with ünly One Variable 23 Cost Function (Objective Function) 24 Using Elemenlary Calculus lo Aid in Optimum Design 27 Practica! Considerations and Constrai nts 28
Attributes of Good Design 29 Design Research and Computei-Bascd Models of Design Pvoeesses 29 A Few Suggestions for Writing Computer Programs 30 Working "Smarter" and Designmg "Smarter" 30
References and Bibliography 31
Design Problems 31
Chapter 2 Materials for Machine Design 33 Material Properües Required in Design 34
The Tensile Test 35 Resilience 37
Toughness 37 Compressive Strcngth 38
Hardness 38 lmpact Strenglh 41 Fatigue Strcngth and Endurance Limit 42 Homogeneity and Tsotropy 45 Engineering Design Implications 47
Specific Materials 47 Plastics 48
Tension Test 49 Tensile Modulus 50
Bending 50 Bending Stress 51
Safety Factor 53 Selected Types of Plastics 53
Nylon 53 Liquid-Crystai Polymer Plastics 54 Polyphenylene Sulfide (PPS) 54 Injection-Moldablc Polyethylene Terephalates (PET) 54 Long-Fiber-Reinlbrced Thermoplastics 54 Polyarylate 54
Phenol ics 54 Polycarbonates 54
Contents • ix
Steel 56
Alloying Elements 57
Steel Designations 57
Carbon Steel 58
High-Slrength Low-Alloy Steel 58
Quenched and Tempered Alloy Steel 58
Ultrahigh-Strength Steel 58
Properties Typicai of Steel 59
Heat Treatment of Steel 59
Gast Iron 60
Stainless Steel 61
Aluminum and Aluminium Alloys 61
Other Nonferrous Engineering Metals 62
Powdcr Metallurgy 63
P/M Part Design Considerations 65
Structural Ceramics 66
Composite Materials 66
Elastomers 69
Databases and Experl Systems 70
A Database/Expert System: Interactive Software for
Material Seleclion 7 1
References and Bibüography 74
Design Problems 75
Chapter 3 Static Stresses in Machine Members andFaüure Theories for Static Stress 77
Static and Time-Varying Stresses 78
Working Strength and Factor of Satety 78
Uniform Tension 78
Stress Duie to Bending 79
Shear Stress Due to Bending 81
Torsion 83
Bending and Direct Tension 83
Stress at a Point 84
Normal Stress 84
Shcar Stress 84
Combined Stress 85
Principal Stresses 85
x • Contents
Principal Stresses: Plane Stress Case 86 The Maximum Normal Stress Theory 86 Maximum Shear Stress: Plane Stress Case 87 Mohr Circles for Plane Stress 88 The Maximum Shear Stress Theory 90 The von Mises Theory 91 Which Failure Theory Ts the Best? 94 Principal Stresses: The Three-Dimensional Case 95 Failure Theories for Three-Dimensional Static Stress Fielcls 96 References and Bibliography 97 Design Problems 98
Chapter 4 Dynamic Loading of Machine Members (Design for Endurance) 100
Failure Theories for Fatigue Loading 101
Reversed Stress 101 Approximating Fatigue Strength and Endurance Limit 102 Endurance Limit: Corrections for Actual Design Conditions 102
Surface Roüghness 103 Size Effects 104
Stress Concentration 104 A Note on Noteh Sensitivity and Stress Concentration 105 Comparing the Effects of Static and Fatigue Loading 106
Theoretical Stress Concentration Factors for Design 107 Plate in Tension with a Central Hole 107 Plate in Bending with a Central Hole 107 Axisymmetric Case 108
Biaxial Tension 109 Biaxial Stresses with Opposite Sign 110 Elliptical Holes 110 Stepped Shafts 110
Reducing Stress Concentration 112 Statistical Distribution of Data: Reliability 113
Normal Distributions 113 Reliability Factor 114 Failure Rate and Samples-Per-Failure Ratio 114
Corrected Endurance Limit 116 Rotating Shafts Subject to Bending 119 Design for Fatigue Loading with Mean and Range Stress 120
Contents • xi
Soderberg Criterion 122
A Note on Design for Fatigue Loading 124
The Goodman and Gerber Criteria for Fatigue Loading 125
The Goodman Criterion 125
The Goodman-Yield Criterion 125
The Gerber-Yield Criterion 125
Probabi lity Theory with Potential Applications to Machine Design 127
Tndependent Events 127
Mutually Exclusive Events 127
System Reliabiiity (Reliability When Several Components Are
Tnvolved) 128
Redundant Components (Parallel Systems) 1 28
Series Systems 128
Hirns for LJse of Regression Analysis to Obtain Design Equations 129
Logarithmic Regression 130
Exponenüal Regression 130
Power Regression 131
Improving Resistance to Fatigue ! 32
Shot-Peening 132
References and Bibliograph}' 134
Design Problems 134
Chapter 5 Bending of Machine Members 137
Beams with Concentrated and Distributed Loads 138
Support Reactions 139
Equilibrium of Statically Determinate Beams 139
Shear Force and Bending Moment 139
Singularity Functions Applied to Machine Design 141
Singularity Functions in a Computer Program 144
Singularity Functions Applied to Shear and Moment in Machine
Members: Integration of Singularity Functions 144
Bending Stress 147
Assumplions and Limitalions 147
Locating the Neutral Axis 148
Calculating Momenl-of-Inertia 151
Moment-of-lnerüa of Seclions That Are Not Symmetrical about the
Neutral Axis 155
Locating Bearings and Olher Supports 157
xii • Contents
Beam Defiection 161 Stepped Shafts and Beams 162 Design of Bending Members 166 Rcferences and Bibliography 170 Design Problems 170
Chapter 6 Finite Element Analysis 173
Modeling a Real Problem: Loading 174
Saint Venant's Principle 174 Model Geometry 175 Three-Dimensional Stress Fields and Plane Stress 175 Symmetry 176
Symmetry Boundary Conditions 176 Axi Symmetrie Problems 177 Finite Element Types 177 Nodes 178 Finite Element Mesh Generation 179
Element Size 179 Aspeet Ratio 180
Preprocessing 180 The Solution Phase 180 Postprocessing 181 Modeling Actual Machine Design Problems: Interpretation and
Verification of Results 194
Verification 195 Interpretation 195
References and Bibliography !95 Design Problems 196
Chapter 7 Eiastic Stability (Column Bückling) 198
The Eu\er CoYwin 199 Moment-of-Inertia and Radius of Gyration 202
Radius of Gyration 203
End Conditions 204 Clamped-Free Columns 204 Clamped-Clamped Columns 205 Clamped-Pinned Columns with Lateral Restraint 205 Clamped-Clamped Columns with Lateral Restraint 206
Contents • xiii
Idcnüfying Slender Columns and Short Columns 207 Special Considerations in the Design ot' Compression Members 209
References and Bibliography 210
Design. Problems 210
Chapter 8 Shaft Design 212
Normal and Shear Stress in Rotating Shafts 213
Torsional Stress 213
ßending Stress 214 Shafts Subject Only to Torsion 2.14
Principal Stresses for Pure Torsion 215 Maximum Normal Stress Theory 215 Maximum Shear Stress 215 Maximum Shear Stress Theory 215
von Mises Stress 216 Power and Torque 216 Hollow Shafts 217 Rotating Shafts Subject Only to Bending 219 Bending and Torsion Loads on Rotating Shafts 221 Soderberg-Maximum Shear Criterion 222 Soderberg-von Mises Criterion 223 Shaft Loading Due to Belt and Chain Drives 223
Torque 223 Tension Ratio 223 Bearing Reactions 224 Shear and Bending Moment 224
Singularity Function 224
Concentrated Loads 224 Singularity Functions for n ä ( ) 224
Distribuled Loads 225 Integration of Singularity Functions 225 Defining the Singularity Function for Computer Use 225
Shear Force 225 Bending Moment 226
Shaft Loading in Two Planes 231 A Few Notes on Shaft Design 236 Design Problems 237
xiv • Contents
Chapter 9 Gears 240
Types of Gears 241 Choosing Drive Train Elements 242
Spur Gears 243 Spur Gear Terminology 243
Speed Ratio for Nonplanetary Gears 246 Rack 247
Involute Tooth Form and Line-of-Action 247 Pressure Angle and Base Circle 247 Addendum and Dedendum 248 Interference Points and Interference 249
Maximum Allowable Addendum Based on Interference 249 Redesigning to Eliminate Interference 251
Contact Ratio 251
Interference in Rack and Pinion Drives 254 Power and Torque 256 Tooth Loading on Spur Gears 256 Countershafts 257 Shaft Design 260 Gear Tooth Failure 263 American Gear Manufacturers Association (AGMA)
Technical Standards 264 Selection of Materials and Material Treatment for Gearing 264
Quality Number 265 Design Based on the Bending Strength of Gear Teeth 266
Design Factors 266 Application Factor 266 Dynamic Factor 266 Load Distribution Factor 269 Bending Strength Life Factor 270 Reliability Factor for Bending Strength 270 Temperature Factor 270 Size Factor 270 Geometry Factor for Bending Strength 271 Load Sharing 271 Analytical Approximation of Geometry Factor for Bending 273 Allowable Bending Stress Number 273
Computer-Aided Design Procedure Based on Bending Strength 274
Contents • xv
Design Based on Pitting Resistance of Gear Teeth (Wear) 275 Design Factors for Pitting Resistance 275 Application Factor, Dynamic Factor, Load Distribution Factoi-, Reliability
Factor, Temperature Factor, and Size Factor 275
Pitting Resistance Life Factor 276
Hardness Ratio Factor 276
Elasticity Factor 276 Surface Condition Factor 277 Calculaling the Pitting Resistance Geometry Factor 277
Allowable Contact Stress Number 278 Computer-Aided Design Proccdure Based on Pitting Resistance 279
Evaluating the Results of the Design Based on Bending Slrength and the Results of the Design Based on Pitting Resistance 279
Helical Gears on Parallel Shafts 284 Tangential, Radial, and Thrust Loads 287
Helical Gears on Crossed Shafts 294 Worm Drives on Pcrpendicular Shafts 295
Self-Locking and Overrunning Drives 298 Tangential, Radial, and Thrust Loads for Wonn Drives on Perpcndicular
Shafts 298 Bevel Gears 299
Tooth Loading of Bevel Gears on Pcrpendicular Shafts 301 Power and Torque 301
Planetary Gear Trains 302 Balanced Planetary Trains 303
Speed Ratios 304 The Simple Planetary Train as a Speed Changer 305 Torque and Tooth Loading in a Planetary Train 305
Conditional Functions 31.0 References and Bibliography 311 Design Problems 311
Chapter 10 Belt Drives 315
Speed Ratio 316 Belt Drive Geometry: Contact Angle and Belt Lcngth 316 Power, Rotational Speed, and Torque 318
Belt Tensions 319 Inerti a Effects 319
xvi * Contents
V-Belts 319 V-Belt Drive Capacity 320 Service Factor and Design Power 320 Drive Sheaves and Idlers 320
V-Bell Drive Design and Sclcction 324 Alternative Design Procedure for Multiple V-Belt Drives 326
Regression Analysis: User-Written Programs 33.1 Fiat Belts 333
Fiat Bclt Drive Capacity 333 Synchronous Belt (Tiniing Belt) Drives 336 Variable-Speed Drives 337 Design Problems 337
Chapter 11 Chain Drives 340
Drive Selection 341 Roller Chain 342
Pitch and Pilch Diameter 343 Speed Ratio and Chain Velocity 343
Roller Chain Power Rating 345
Low-Specd Failure 345
High-Speed Failure 345 Power Ratings 346 ANSI Designation, Pilch, Slrength, and Peak Power Rating 347 Service Factors and Design Power 348
Design and Selection of Roller Chain 349
Design for Single-Strand Chain 350 Design of Mulliple-Strand Chain Drives 351
Silent Chain 353 Factors for Choosing Single-Pin or Two-Pin Silent Chain 353
Power, Torqne, Tension, and Speed 355
Chain Lenglh and Center Distance 355 Power Ratings for Silent Chain Drives 356 Service Factors and Design Power for Silent Chain Drives 358
References and Bibliography 362 Design Problems 363
Chapter 12 Clutches 364
Di sc Clutches 365 Applications of Single- and Double-Throw Clutches 365
Contents • svii
Power and Torque 367 Torque Capacity of a Guten 368 Actuating Force 369 Loading Factor 372 Design and Specificalion of Disc Clutches 372 Engine Performance 378 Design Problems 380
Chapter 13 Brakes 382
Typcs of Brakes 383 Kinetic Energy and Potential Energy 383
Energy Due to Braking 384
Total Energy 384 Calciüation of Mass-Moment-of-Incitia 385
Radius of Gyration 385 Hoists and Olher Materials-Handling Machinery 386 Vehicle Brakes 387
Reaction and Response Time 388 Caliper Disc Brakes 390 Caliper Brake Design 392 Drum Brakes 393 Drum Brake Analysis 394
Primary Shoe (Sclf-Actuating Shoe) 394
Secondary Shoe 396 Drum Brake Design Oplions 398 Clutch-Type Disc Brakes 399 Band Brakes 399 Belays 401 Reference 402 Design Problems 402
Chaptcr 14 Power Screws and Linear Actuators 405
Ball-Serews 407 Linear Motion Systems 407 Special-Application Power Screws and Linear Actuators 407 Pitch, Lead, and Lead Angle 410
Thread Form 410 Power Scrcw Efficiency 411 Bevel and Worrn Drives for Power Screws 413
xviii * Contents
Positioning Precision and Linear Velocity 413 Output and In put Power 414
Input Torque Requirement 414 Screw Reaction Torque 415
Elastic Stability (Bückling) of Power Screws 418 The Euler Column Design Criterion 418 Other Boundary Condilions 418
Miter Gear Boxes and Multiple Lifting Systems 419 Design Problems 421
Chapter 15 Fasteners 423
Joint Failures 424 Fastener Materials 424
Threaded Fasteners 425 Bolted Joints in Tension 425
Joint Design for Staue Tensile Loads 426
Prcloading Bolted Joints for Fatigue Load Sharing 429
Determination of Optimum Preload and Evaluation of the Decision 431 Stiffness and the Effect of Gaskets 432 Evaluation of Preloaded Joints 432
Shear Loading of Fasteners 436 Double Shear 436 Bearing Failure 437
Joint Design for Symmetrie Load 438 Joint Efficicncy 438 Optimum Joint Design 439
Shear Loading of Bolted Joints 439 In-Plane Eccentric Loads 439
Centcr-of-Gravity of a Fastener Group 440 Torque 440 Moment-of-Inertia 441 Fastener Load 441 Bearing on the Plate 442
Design for Symmetry 445 Fasteners with Out-of-Planc Loads 447
Moment-of-Tnertia 448 Tensile Load 448 Shear- Load 449
Contents • xix
Fastener Selection 449 Fastener Types 449
SteeJ Bolts with Nuts or Tapped Holes 450 Self-Drilling Screws 450 Rivets 450 Blind Rivets 451 Threaded Inserts and Caged Nuts 451 Self-Locking Screws and Nuts and Other Locking Methods 452 Snap-In Design 455
References and Bibliography 456 Design Problems 456
Chapter 16 Welds and Adhesive Joints 458
Shielded Metal Are Welding (SMAW) 459 Submerged Are Welding (SAW) 459 Gas Metal Are Welding (GMAW) 460 Gas Tungsten Are Welding (GTAW) 461 Resistance Welding (RW) 461 Laser Beam Welding (LBW) 461 Electron Beam Welding (EBW) 461 Friction Welding (FRW) 462 Ultrasonic Welding (USW) 462
Other Ultrasonic Joining and Forming Techniques 463 Vibration Welding 464 Selection of Welding Methods 464 Butt Joints 464 Fillet Welds 465 Design of Welds with Out-of-Plane Eccentnc Loads 467
Direct Shear 468 Moment-Induced Shear 468
Moment-of-Inertia 468 Determination of Required Weld Size 469 Units Used in Weld Design for Eccentric and Out-of-Plane Loads 469
Out-of-Plane Loads on Asymmetrie Weld Groups 470 Welds with In-Plane Eccentric Loads 473
Center-of-Gravity and Moments-of-lnertia 473
Torque 474 Weld Stress 474
xs • Contents
Required Weld Size 475 Welding Symbols 477 Adhesives 477
Adhesives Terminology 477 Advantages of Adhesives 478 Special Considerations for Designs Incorporating Adhesives 479
Adhesive Selection 479 Adhesive Tests 479
Tensile Tests 480 Joint Design 481
Lap Shear Tests 481 Peel Tests 482
References and Bibliography 482 Design Problems 483
Chapter 17 Springs and Torsion Bars 485
Torsion Bars 486 Bar Diameter for Static Loading 487 Working Strength 487 Bar Length 488
Helical Compression Springs: Design for Static Loading 490
Shear Stress 491 Determination of Wire Diameter Based on Stress 491
Spring Rate 491 Active and Inactive Coils 492 Specification of Active Coils Based on Spring Rate and
Deflection 492 Free Height, Solid Height, and Clash Allowance 492
Helical Compression Springs: Design for Fatigue Loading 496
Testing and Service Loading of Spring Materials 496 Allowable Mean Shear Stress 497 Calculating Optimum Wire Diameter for Fatigue Loading 498 Determining Spring Height 498
Designing the Spring Analytically 499 Helical Extension Springs 502
Determining Wire Diameter 502 Spring Rate and Preload 503
Active Coils 503
Contents • xxi
Leaf Springs 503 Cantilever Spring 504 Simply Supported Spring 504 Multileaf Springs 504
Air Springs 506 Disc Springs 507
Load and Deflection 508 Stacking Disc Springs in Parallel and Series 509
Spring Li nearity 510 Vibration Transmissibility and Isolation 510
Natural Frequency 511 Vibration Damping 5!2 Vibration and Shock Isolation 512
Motion Transmissibility 513 Force Transmissibility 513 Selection of Spring Mounts to Limit Motion or Force
Transmissibility 515 References and Bibliography 518 Design Problems 518
Chapter 18 Bearings and Lubrication 520
Friction 521 Coefficient of Friction 522 Friction and Dissipation of Energy 522
Ball Bearings 523 Load Distribution 523
Ball Bearing Load Carrying Capacity 525
Basic Load Rating of Ball Bearings 525 Ball Bearing Life Expectancy 528
Reliability 529 Life Adjustmenl Factor for Reliability 529
Ball Bearing Selection from Manufacturers' Catalogs 534 Special Considerations for Ball Bearing Selection 535
Outer Race Rotation 535 Thrust Loads 535 Rating Criteria 535 Environmental Conditions, Materials, and Loading 535
Static Load Rating of Ball Bearings 535
xxii • Contents
Roller Bearings 536 Bcaring Seals 538 Linear Motion Systems 538 Lubriealion 538
Lubricaüon Regimes 539 Hydroslalic Lubriealion 540 Beariüg Selection 540 Lubrieant Viscosity 541 Hydrodynamic Lubncation: Design for Light Loads 544
Hydrodynamic Lubncation: Design for Heavy Loads 548 Ecccnlricity and Torque Calculaüon Using Regression Eqiiations 552
Referenccs and Bibliography 558 Design Problems 559
Chapter 19 Design for Manufacture 562
Concurrent Engineering 563 Manufacturing Processes 563 Computer-Aided Manufacturing 564
Numerical Controi 564 Flexible Manufacturing: Robots and Manipulators 565
Design for Ease of Manufacture and Assembly 565
Reducing the Number of Parts in a Product 566 Slandardization 567 Symmelry 567
Asymmelry 567 SJotted Holes 567
Design for the Environment (DFE) 569 Prototypes 570
Computer Solid Models 570
Machined Prototypes 570 Stereolilhography 571 Other Rapid Protolyping Methods 572
Robust Design and Variabilily Reduction 572 Evaluating Quality Improvement. 573
The Cost of Product Failures and Rejeets 573 Target Measurements and Tolerances 573 Product Tests and Measurements 573 Useful Statistical Descriptors 574
Contents • xxiii
Probability 574 Probability of a Reject 574 The Normal Curve 575 Cost Calculation 575
Design and Manufacturing Alternatives 577 Cost Saving by Centering the Process 577 Reducing Output Variation and Increasing Tolerances 579 Problems Involving One Tail of the Normal Distribution Curve and
Problems Involving Two Tails 579 Probability of a Reject for a Centered Process 580
References and Bibliography 582 Design Problems 582
Chapter 20 Special Topics in Machine Design 584
Environmental Concerns 585 Energy Use 585 Conservation of Energy and Other Resources 585 Global Warming and Air, Water, and Noise Pollution 586
Design for Safety in Manufacturing 594 The Occupational Safety and Health Act and the Occupational Safety
and Health Administration 594
Mechanical Hazards 595 Machine Guarding 595
Industrial Noise 597 Product Safety and Product Liability 602
Guidance for Safe Design 602 Design Implications of Case Reports 603 Guards and Special Safety Features 605
Unforeseen Circumstances 606 Product Recall 607
Product Liability 607 Expert Testimony and Reports 609
Patents and Trade Secrets 610 Types of Patents 610
Inventor's Records 610
Patentability 610 Trade Secrets 611 Ownership and Säle of Patent Rights 611
xxiv • Contenls
Ethics 611 Ethical Practice 611 Ethical Quesüons 612 Whistle Blowers 612
Economic Decisions 613 Compound Interest 613 Time Required to Increase Principal by a Givcn Percenl 613 Rules of Thumb for Interest, Time, and Tncrcase in Principal 614 PresentValue 615 Annual Cost of an Investment 617
An Introduction to Optimization 619 Cost Function and Conslraints 620 Multivariable Optimization Problems 620
Rcferences and Bibliography 626 Design Problems 627
Appendix Machine Design Projects 631
Sourccs of Project Ideas 631
General Considcrations 631 Suggestions for Project Proposais and Reports 631
Suggested Project Topics 632 Human-Powered Vehicle 632 Reverted Gear Train 632 Machine Guarding 632
Lubrication 632 Brake Noise 633 Laboratory Experiment 633 Crash Protection for Side Impact 633 Pedestrian Safety for Light-Rail Systems 633 Energy-Absorbing Structure for Trucks 633 Device to Aid Persons with Disabililies 633
Pipeline Valve 633 Aircraft Door Latch 633 Seat-Beil Mechanism 634 Transportation for People with Disabilities 634 Database/Expert System for Selection 634
Partial Answers to Selected Problems 635
Index 641